- Research team led by CRAG researcher Ana Caño-Delgado obtains plants resistant to water scarcity
- A modification of the steroid hormone signalling enables to obtain a drought resistant plant without affecting plant growth
- Researchers work to translate this advance to cereals and horticultural species
Drought and its impact
Extreme drought episodes and heatwaves are among the effects of climate change that are becoming clearly visible. These effects have a definite impact on vegetation, including by that an impact on agriculture. The decrease in rainfall and the abnormally hot temperatures in northern and eastern Europe have caused large losses in cereals and potato crops and in other horticultural species in the immediate and recent past. It is claimed that at least 40% of crop losses worldwide are due to drought, a proportion that might rise enormously as a result of climate change.
Experts have long warned that to ensure food security it is becoming necessary to use plant varieties that remain productive in drought conditions. Drylands, areas characteristically having a scarcity of water, will be increasing in extension in the future, as global temperatures increase. Previously wet areas may become increasingly dry. The plants present, including crops, will become subject to conditions of stronger hydric stress, posing a challenge to their growth –and in extreme cases, their survival-.
For agriculture, severe droughts are a serious threat, potentially resulting in a strong impact to the food supply, even resulting in famine episodes in affected countries. Such events have already been recurrent in a number of regions across the world, for instance in Ethiopia, Somalia or the African Sahel region that spans from Mauritania, Mali, Chad, Niger and Burkina Faso to parts of some of the countries to the South.
A basic research biotechnological approach... for a tangible solution
Bearing in mind the problems posed to agriculture by increasing number and intensity of droughts, a team led by researcher Ana Caño-Delgado, of the Center for Research in Agricultural Genomics (CRAG) have researched on the engineering of plants resistant to drought. The team of Caño-Delgado has obtained plants with an enhanced resistance to hydric stress, by acting on the signalling pathway of the plant steroid hormones known as brassinosteroids. The study, published in the journal Nature Communications, is the first to find a strategy to increase hydric stress resistance without affecting overall plant growth.
Brassinosteroids are involved in numerous plant processes including cell expansion and elongation, vascular differentiation, pollen tube formation, senescence, cell division and cell wall regeneration, and the resistance to chilling and drought. These hormones bind and are perceived by different plasma membrane-located receptor proteins, causing in turn the relay of a signal in the cell that ends up producing effects such as cell elongation or division. One of these receptor proteins is the protein BL3 , object of the study.
Ana Caño-Delgado has been studying how the plant steroids (brassinosteroids) regulate plant development and growth in the model plant Arabidopsis thaliana for more than 15 years. Since 2016, and thanks to a project funded by the European Research Council, the laboratory of Dr. Caño-Delgado uses their accumulated knowledge to find strategies to confer drought resistance to plants. By modifying brassinosteroid signalling, researchers had so far achieved Arabidopsis plants with increased drought resistance, but due to the complex action of these hormones on plant growth, these plants were also much smaller than their unmodified counterparts.
In the work, the researchers have studied drought resistance and growth in Arabidopsis thaliana plants with mutations in different brassinosteroid receptors. The study allowed the researchers to discover that plants that over-express the brassinosteroid receptor BRL3 specifically in vascular tissue are more resistant to the lack of water than control plants. Additionally, unlike other mutants, they do not present defects in their development and growth. As explains Caño-Delgado, "we have discovered that modifying brassinosteroid signaling only locally in the vascular system, we are able to obtain drought resistant plants without affecting their growth”.
At a later stage, CRAG researchers in collaboration with researchers from Europe, the United States and Japan analysed the metabolites in the genetically modified plants. From the obtained data, it was found that Arabidopsis plants overexpressing the BRL3 receptor produce more osmoprotective metabolites (such as sugars and proline) in the aerial parts and in the roots under normal irrigation conditions. These compounds would help to better conserve water in the plant.
When the modified plants were actually exposed to drought conditions, specific protective metabolites would additionally quickly accumulate in the roots, protecting them from drying out. So, the higher amounts of BRL3 resulting from the overexpression would, in a way, be preparing the plant to respond to the situation of water scarcity. This mechanism, known as priming, can be somehow compared to the effect of vaccines in the human body: when actual drought conditions take place, the additional mechanism would be triggered, but the plant would already be better prepared to resist the adversity of drought conditions.
Making the jump from fundamental to applied research: a coming solution for species of agronomic interest?
As said Caño-Delgado, "drought is one of the most important problems in today's agriculture. So far, the biotechnological efforts that have been made to produce plants more resistant to drought have not been very successful, because as a counterpart to enhanced drought resistance there was always a decrease in plant growth and productivity. It seems that we have finally found a strategy that could be applied and we want to continue exploring it ".
The original discovery was done with, Arabidopsis thaliana, a small herb used as a model plant that has no direct application outside of research. The results, however, make way for new developments with a more practical application. The team of Caño-Delgado is already working on applying this strategy on plants of agronomic interest, especially in cereals. If successful, the next steps can could a large impact on agriculture.
Image of Arabidopsis plants exposed to drought stress was made by the researchers and kindly provided by CRAG.